I want to convert my wood burning fireplace into a gas fireplace. The problem I have is my chimney goes up about 4ft via masonry brick with slotted vents then angles to a pipe going through the roof. Problem I have is the two 3 inch co-linear pipe will not fit through the masonry brick slots shown in the pic attached. Somehow I have to enlarge the slots to accommodate the co-linear pipe for the gas fireplace. Any ideas/recommendations? DW